1. Field of the Invention
The present invention relates to a node device, and in particular to a node device which has a function of recognizing network route (path) information.
In recent years, a network which has a traffic processing function and a network routing function and which can support a multiplexed connection has been realized with an advance of a communication technique.
For example, a node device in which a PNNI (Private Network to Network Interface) specified by the ATM Forum is installed can grasp a network status such as a resource or a topology, and select the optimum route or path upon setting a connection by periodically or non-periodically transmitting/receiving network route information within the own node device to/from the adjoining node device.
In such a network, it is required to set the connection of the optimum route based on a selection reference corresponding to a user's demand such as Quality of Service (hereinafter, occasionally abbreviated as QoS).
2. Description of the Related Art
FIG. 18 shows an arrangement of a prior art node device. This node device 11 is composed of a route information transmitting/receiving portion 24 which transmits/receives route information 77 to/from a node device 12 through a communication line 40, a route information managing portion 23 which transmits/receives the route information 77 with a transmitting signal 75 and a receiving signal 76 through the transmitting/receiving portion 24 to be stored and managed as route information 70, a route selector 22 which selects a route based on the route information 70 (hereinafter, occasionally referred to as resource information) obtained by exchanging a route information inquiring signal 73 and a response signal 74 with the managing portion 23, and a call processor (processing portion) 21 which sets and releases a connection passing a route obtained by exchanging a route inquiring signal 71 and a response signal 72 with the selector 22.
This arrangement is similarly applied to ATM node devices in which the resource information of the own node device is exchanged with the other by the PNNI protocol.
FIG. 19A shows a network example composed of ATM node devices 11-15. The node devices 11 and 13 are connected with a route 51 passing the node device 12 and a route 52 passing the node devices 14 and 15. The node devices 11 and 13 respectively accommodate terminals 31 and 32.
The route information managing portion 23 of each node device periodically advertises the holding resource information (available cell rate, delay, and the like) of the trunk circuit of the own node device to the adjoining node devices through the route information transmitting/receiving portion 24 by the PNNI protocol, and receives the resource information transmitted from the other node devices through the route information transmitting/receiving portion 24 to hold the same in the route information 70 as database information.
Also, the route information managing portion 23 of each node device further advertises the resource information received from the other node devices to the adjoining node devices. Thus, each of the node devices can hold the resource information of all the node devices within the PNNI network.
Furthermore, when the network formation is changed by the PNNI protocol, the route information managing portion 23 can detect the fact for the notification between the node devices that the information within the network has been changed. Accordingly, the present network formation can be grasped as the route information.
FIG. 19A shows an “available cell rate” (unit: cps (cell per second)) (hereinafter, occasionally abbreviated as ACR) between the node devices, and a “cell transfer delay” (unit: μs) (hereinafter, occasionally abbreviated as CTD) between the node devices included in the route information 70 which the route information managing portion 23 of each node device holds.
For example, the ACR in the direction of node device 11→node device 12 is 15000 cps, and the CTD is 5 μs. The ACR in the direction of node device 12→node device 11 is 12000 cps, and the CTD is 4 μs. These ACR's and CTD's change according to the resource status.
When the connection setting is demanded, the route selector 22 recognizes, based on the database prepared from the resource information, how many routes there are from the own node device to the destination node device at that time, and determines the most advantageous route in the routes based on e.g. a quality of service (delay, cell delay variation, and the like) preset.
The operation example of the route selection upon setting the connection between the node devices 11 and 13 will now be described.
The call processor 21 of the node device 11 inquires of the route selector 22 the connection setting route up to the node device 13 by the route inquiring signal 71. The route selector 22 inquires of the route information managing portion 23 the route information to the node device 13 by the route information inquiring signal 73 to obtain topology information as the response signal 74.
Based on this topology information, the route selector 22 recognizes that there are two candidates of the route to the node device 13.
FIG. 19B shows the route candidates from the node device 11 to the node device 13. Namely, as the route from the node device 11 to the node device 13, there are two routes, i.e. the route 51 (node device 11→12→13) and the route 52 (node device 11→14→15→13). The ACR and CTD of the route 51 are respectively 5,000 cps and are 10 μs, and those of the route 52 are respectively 15,000 cps and 20 μs.
The ACR of each route indicates the minimum value of the available cell rates on the route, and the CTD indicates the total value of the CTD's on the route.
The route selector 22 of the node device 11 selects the route 51 with the smaller CTD between the two route candidates as the optimum route and responds to the call processor 21 by the response signal 72. The call processor 21 sets the connection passing the route 51 with respect to the node device 13.
It is general to realize the interworking between the current IP network and ATM network by the connection which does not consider the QoS, i.e. which uses UBR (Unspecified Bit Rate) for a service category (LANE 1.0, MPOA 1.0, and the like prescribed by the ATM Forum).
However, with the future extension of the IP network application, some QoS guarantee in the IP network becomes an important issue. Accordingly, the demand for the interworking between the IP network and the ATM network will extend, so that the cooperation of the ATM network relating to the QoS guarantee becomes important (in MPOA 1.0, QoS is supported by the negotiation function of non-realtime VBR (Variable Bit Rate)).
Protocols such as Diffserve (differentiated services) and RSVP (resource ReSerVation Protocol) relating to the QoS guarantee have been proposed in the IP network whereas in view of the installation thereof, its scale becomes large and so unrealistic.
As a proposal for a simple achievement of the installation, an ATM network where the ATM is made a backbone to guarantee the QoS can be mentioned.
However, by a route selection method in the ATM network, upon setting the connection between the node devices, the optimum route for satisfying conditions such as QoS is selected from the available routes to set the connection. Therefore, even when the network topology changes after setting the connection and more optimum route becomes available, a disadvantageous route set upon setting the first connection should be kept being used. Alternatively, the connection setting can not be made because the QoS can not be satisfied from the beginning.
Moreover, as for the IP data it is often thought from its character that the connection should be set by using a temporarily available route even if it does not completely satisfy the QoS, so that it is thought effective that a flexible route selection can be performed by switching the route over to another which satisfies the QoS when it becomes available.
Namely, by the above-mentioned reason, the prior art route selection processing has been limited only for the connection setting, so that there has been a problem that even when a more advantageous route becomes available the route selection can not be performed again.
As measures for solving this problem, in the Japanese patent publication laid-open No.10-93567, the node device which has detected the change of the route information notifies the terminal on the transmitting side that an optimum route becomes available, so that the terminal on the transmitting side performs the call setting again to try again the connection setting on the optimum route. Thus, the switchover to the optimum route corresponding to the change of the route information can be realized.
However, in order to notify the terminal on the transmitting side of the route information change and to try again the connection setting on the optimum route on the terminal side, the development of a new protocol and the installation of the concerned protocol in the terminal are required, which can not be regarded as realistic measures.